1. Field of the Invention
The invention relates to an anchoring structure for use in minimally invasive bioprosthetic heart valve replacement systems. More particularly, the invention relates to a tubular anchoring structure with an inflow end that includes a concave landing zone that reduces paravalvular leakage.
2. Description of the Related Art
The transport of vital fluids in the human body is largely regulated by valves. Physiological valves are designed to prevent the backflow of bodily fluids, such as blood, lymph, urine, bile, etc., thereby keeping the body's fluid dynamics unidirectional for proper homeostasis. For example, venous valves maintain the upward flow of blood, particularly from the lower extremities, back toward the heart, while lymphatic valves prevent the backflow of lymph within the lymph vessels, particularly those of the limbs.
Because of their common function, valves share certain anatomical features despite variations in relative size. The cardiac valves are among the largest valves in the body with diameters that may exceed 30 mm, while valves of the smaller veins may have diameters no larger than a fraction of a millimeter. Regardless of their size, however, many physiological valves are situated in specialized anatomical structures known as sinuses. Valve sinuses can be described as dilations or bulges in the vessel wall that houses the valve. The geometry of the sinus has a function in the operation and fluid dynamics of the valve. One function is to guide fluid flow so as to create eddy currents that prevent the valve leaflets from adhering to the wall of the vessel at the peak of flow velocity, such as during systole. Another function of the sinus geometry is to generate currents that facilitate the precise closing of the leaflets at the beginning of backflow pressure. The sinus geometry is also important in reducing the stress exerted by differential fluid flow pressure on the valve leaflets or cusps as they open and close.
Thus, for example, the eddy currents occurring within the sinuses of Valsalva in the natural aortic root have been shown to be important in creating smooth, gradual and gentle closure of the aortic valve at the end of systole. Blood is permitted to travel along the curved contour of the sinus and onto the valve leaflets to effect their closure, thereby reducing the pressure that would otherwise be exerted by direct fluid flow onto the valve leaflets. The sinuses of Valsalva also contain the coronary ostia, which are outflow openings of the arteries that feed the heart muscle. When valve sinuses contain such outflow openings, they serve the additional purpose of providing blood flow to such vessels throughout the cardiac cycle.
When valves exhibit abnormal anatomy and function as a result of valve disease or injury, the unidirectional flow of the physiological fluid they are designed to regulate is disrupted, resulting in increased hydrostatic pressure. For example, venous valvular dysfunction leads to blood flowing back and pooling in the lower legs, resulting in pain, swelling and edema, changes in skin color, and skin ulcerations that can be extremely difficult to treat. Lymphatic valve insufficiency can result in lymphedema with tissue fibrosis and gross distention of the affected body part. Cardiac valvular disease may lead to pulmonary hypertension and edema, atrial fibrillation, and right heart failure in the case of mitral and tricuspid valve stenosis; or pulmonary congestion, left ventricular contractile impairment and congestive heart failure in the case of mitral regurgitation and aortic stenosis. Regardless of their etiology, all valvular diseases result in either stenosis, in which the valve does not open properly, impeding fluid flow across it and causing a rise in fluid pressure, or insufficiency/regurgitation, in which the valve does not close properly and the fluid leaks back across the valve, creating backflow. Some valves are afflicted with both stenosis and insufficiency, in which case the valve neither opens fully nor closes completely.
Because of the potential severity of the clinical consequences of valve disease, numerous surgical techniques may be used to repair a diseased or damaged heart valve. For example, these surgical techniques may include annuloplasty (contracting the valve annulus), quadrangular resection (narrowing the valve leaflets), commissurotomy (cutting the valve commissures to separate the valve leaflets), or decalcification of valve and annulus tissue. Alternatively, the diseased heart valve may be replaced by a prosthetic valve. Where replacement of a heart valve is indicated, the dysfunctional valve is typically removed and replaced with either a mechanical or tissue valve.
In the past, one common procedure has been an open-heart type procedure. However, open-heart valve repair or replacement surgery is a long and tedious procedure and involves a gross thoracotomy, usually in the form of a median sternotomy. In this procedure, a saw or other cutting instrument is used to cut the sternum longitudinally and the two opposing halves of the anterior or ventral portion of the rib cage are spread apart. A large opening into the thoracic cavity is thus created, through which the surgeon may directly visualize and operate upon the heart and other thoracic contents. Replacement heart valves typically include a sewing ring and are sutured into the annulus, resulting in a time intensive surgical procedure. The patient is typically placed on cardiopulmonary bypass for the duration of the surgery.
Minimally invasive valve replacement procedures have emerged as an alternative to open-chest surgery. A minimally invasive medical procedure is one that is carried out by entering the body through the skin or through a body cavity or anatomical opening, but with the smallest damage possible to these structures. Two types of minimally invasive valve procedures that have emerged are percutaneous valve procedures and trans-apical valve procedures. Percutaneous valve procedures pertain to making small incisions in the skin to allow direct access to peripheral vessels or body channels to insert catheters. Trans-apical valve procedures pertain to making a small incision in or near the apex of a heart to allow valve access. The distinction between percutaneous valve procedures and minimally invasive procedures is also highlighted in a recent position statement, Vassiliades Jr. T A, Block P C, Cohn L H, Adams D H, Borer J S, Feldman T, Holmes D R, Laskey W K, Lytle B W, Mack M F, Williams D O. The clinical development of percutaneous heart valve technology: a position statement of the Society of Thoracic Surgeons (STS), the American Association for Thoracic Surgery (AATS), and the Society for Cardiovascular Angiography and Interventions (SCAI). J Thorac Cardiovasc Surg 2005; 129:970-6).
As valves are implanted less and less invasively, the opportunity for suturing the valves around the annulus is reduced. However, a smaller number of sutures may increase the chance of paravalvular leakage (PVL), i.e. leakage around the valve. A smaller number of sutures may also increase the opportunities for migration and valve stability when placed in-vivo.
Tehrani discloses a superior and inferior o-ring for valve implantation in US Patent Application Publication No. 2006/0271172. Such o-rings cover the entire length of the valve and can therefore not easily be placed within the aortic sinus region. The o-rings presented by Tehrani would also block coronary outflow and adversely affect valve dynamics. The non-circular nature of the o-rings also reduces the radial force needed to adequately conform to irregularities within the implantation site, and is thus not optimal for preventing PVL and migration. The large size of the o-rings disclosed by Tehrani is also not practical as they cannot easily be collapsed down, something that is necessary for minimally invasive valve implantation.
Surgical heart valves include a sewing cuff for direct attachment to the native annulus where the surgeon relies on visual identification to correctly place the inflow ring in the annulus. Minimally invasive heart valves, however, lack any defined feature that interfaces directly with the annulus, instead relying on radial force to hold the valve in position in an attempt to prevent paravalvular leakage. Other conventional designs rely on a “feeler” to locate the native leaflets and when located deploy the valve below the feeler in an attempt to properly seat the valve in the annulus thereby preventing paravalvular leakage. Yet other conventional heart valves rely on a flange construction in which the flange uses double fabric rings to sandwich the device in the native annulus to prevent paravalvular leakage. However, the double fabric rings require additional surgical time in order for the surgeon to verify that the two rings are placed on opposite sides of the annulus.
In addition, while new less invasive valves produce beneficial results for many patients, these valves may not work as well for other patients who have calcified or irregular annuluses because a tight seal may not be formed between the replacement valve and the implantation site. Therefore, what is needed are methods, systems, and devices for reducing paravalvular leakage around heart valves while preventing valve migration and allowing valve collapsibility.
The invention is directed to solving, or at least reducing, some or all of the aforementioned problems.